1. Technical Field
This application relates to computing devices, and more particularly to the field of providing appropriate quality of service for computing devices.
2. Description of Related Art
Host processor systems may store and retrieve data using storage devices containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels of the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical volumes. The logical volumes may or may not correspond to the actual disk drives.
In a distributed computing environment, multiple storage devices, hosts, and perhaps other computing devices service requests that may be initiated from many independent other devices. For example, a number of independent hosts and other storage devices may request I/O's from a particular storage device. It is useful for the particular storage device to be able to provide appropriate quality of service to each requester. However, without a metric for doing so, it may be difficult for the particular storage device to determine how to order the independent requests from the different requesters.
Furthermore, independent sources may specify quality of service performance goals for disk access requests in the form of a requested number of I/O operations per second (IOSPS) and possibly also an average response time (RT). However, in the case of disk access requests, it may be difficult to provide each independent source of the requests with a minimum quality of service since disk performance for a particular source may not always be predictable when other sources are also making requests.
Accordingly, it is desirable to be able to attain quality of service performance goals for independent sources that make disk access requests.